In recent years, the vast majority of the industrialized world has become telephonically accessible via public switched telephone networks (PSTNs). Nonetheless, there remain significant populations in rural or less developed areas who are not accessible via a PSTN for a variety of reasons relating to economy and geography. In such areas, remote communication has been accomplished by radio communications systems or cellular mobile radiotelephone (CMR) systems.
A conventional radio communications system uses a base station transceiver located at a site for favorable radio propagation and a set of transceivers typically located in remote areas. Most radio communication systems of this type are useful for conducting communications between short distances, such as within the boundaries of a town or city, via a very high frequency (VHF) radio link.
Although conventional radio communications systems are useful for specialized communications applications, two-way radios are not widely accepted for general purpose communications. In many locations, the use of two-way radios is governmentally regulated and the allocated frequency spectrum is relatively limited. Furthermore, the quality of communications is subject to the propagation conditions between communications sites. Additionally, two-way radio equipment is generally large and heavy and, as a result, is unlikely to be carried by a user at all times or to be installed in small or existing equipment.
Another form of two-way communication is a CMR system. Typical CMR systems are characterized by dividing a radio coverage area into smaller coverage areas or “cells” using low power transmitters and coverage-restricted receivers. As shown in U.S. Pat. Nos. 3,906,166 and 4,268,722, the limited coverage area enables the radio channels used in one cell to be reused in another cell. As a cellular mobile radiotelephone within one cell moves across the boundary of the cell and into an adjacent cell, control circuitry associated with the cells detects that the signal strength of the radiotelephone in the just-entered cell is stronger, and communications with the radiotelephone are “handed off” to the just-entered cell. Thus, a CMR system can supply two-way communications for an array of cells, thereby supplying communications for a much wider area than conventional two-way radios.
Use of cellular mobile radiotelephones can pose an appreciable expense to the user. Initially, a cellular mobile radiotelephone must be purchased and an initial registration fee paid to a cellular carrier providing service to the geographic area where the handset will be used. A telephone number is assigned to the newly purchased radiotelephone and a “handset I.D.” is established by the carrier and maintained within the CMR system. The handset I.D. identifies communications from that particular radiotelephone as coming from a subscriber to the cellular carrier's services.
Beyond the initial purchase and cellular carrier connection fees, expenses incurred in ordinary use of such a radiotelephone are even more significant. Historically, every communication placed from a radiotelephone is processed through the CMR system without regard for the location of the radiotelephone when the call is placed. Such processing incurs a combination of usage fees and toll or roamer charges. These fees vary depending upon the location of the radiotelephone relative to the geographic coverage area of the cellular carrier's services subscribed to, as well as other time and geographic related variables. In a basic case, a radiotelephone user who subscribes to a cellular carrier's services in Atlanta and who places a call from within his area of geographical coverage to a party, also located in Atlanta and within the same geographical coverage area, would be assessed a fee for accessing the CMR system, in addition to a per minute usage fee. The same call placed from a conventional telephone linked directly to the PSTN would be deemed a “local call” and would typically generate no per call fees. In a more extreme case, the same subscriber to a cellular service having a geographical service area in Atlanta who is on vacation in Los Angeles and desires to use his radiotelephone to place a call from his hotel room to a restaurant across the street will incur roamer charges for accessing the CMR system outside of his carrier's geographical coverage area, a fee for relaying the call from Los Angeles back to his carrier's mobile switching center in the Atlanta area, a fee for relaying the call from Atlanta back to the restaurant across the street from the caller in Los Angeles, all in addition to a per minute usage fee. Again, had the subscriber placed this call from his hotel room to the restaurant across the street via a conventional telephone linked directly to the PSTN, the call would have been deemed “local” and would have incurred no carrier-related fees.
Until recently, individuals in areas without direct access to the PSTN but desiring telephonic capability were essentially limited to costly and inconvenient CMR systems. Some of the inconvenience of using a home-based radiotelephone have been addressed with the advent of so-called fixed wireless (FWL) systems. FWL systems typically comprise a conventional cellular telephone physically connected to one or more conventional telephone handsets within a discrete location, such as a residence or office. The FWL system allows the connected conventional telephone handsets to access the CMR system through the cellular telephone to which they are connected. Even FWL systems, though, allow virtually no freedom of movement for the user and do not resolve other problems typically associated with CMR systems, including high cost of operation.
Accordingly, there is a need to provide individuals who do not have access to the PSTN a way to communicate telephonically in a reliable and cost-efficient manner. Additionally, there is a need to adapt current FWL systems so as to facilitate the use of such systems in conjunction with existing PSTN elements. Furthermore, there is a need to develop safeguards sufficient to prevent individuals who do not subscribe to a wireless system from gaining unauthorized access to the system, regarding both incoming and outgoing communications.